Iridium, a hard, whitish metal similar to platinum, is extremely rare

Question

Iridium, a hard, whitish metal similar to platinum, is extremely rare on Earth. Extremely high concentrations of iridium on Earth result from only two scenarios: massive volcanic eruptions that release iridium from deep within the Earth and meteorites that shower down on Earth from space. When scientists found concentrations of iridium 30 times higher than normal in rock stratum from 65 million years ago, they concluded that a massive meteor or comet hit the Earth and caused the massive extinction of the dinosaurs.

Which of the following, if true, most strongly supports the scientist’s conclusion?

A. Volcanoes massive enough to generate high concentrations of iridium are very rare.

B. Massive volcanic eruptions occurred frequently 80 million years ago.

C. Most scientists support the hypothesis that a cosmic impact wiped out the dinosaurs.

D. The massive extinction that occurred 70 million years ago killed not only the dinosaurs but also 70 percent of all life on Earth.

E. A comet struck the earth some 120 million years ago, but no widespread extinction occurred.

I think that C supports the conclusion better than B, which is the right answer. I am placing the question before this forum for moot so that I can learn flaws in my thought, if any.

Source: TMH's verbal workbook.

Regards
Rahul.

retro · Accepted Answer

Here is the explanation provided by the guide:

Answer: B. This is a strengthen question. Its conclusion and premises are:
Premises: (1) Extremely high concentrations of iridium on Earth result from only two scenarios: massive volcanic eruptions that release iridium from deep within the Earth and meteorites that shower down on Earth from space. (2) Scientists found concentrations of iridium 30 times higher than normal in rock stratum from 65 million years ago.
Conclusion: A massive meteor or comet hit the Earth and caused the mass extinction of the dinosaurs.

According to the premises, there are two possible causes of high iridium levels. But the conclusion states that one of the causes—a meteor— was definitely the culprit. So the assumption must be that there was not a volcanic eruption that caused the extinction. Once again, you have a causal argument, but now you are going to strengthen it. In order to do so, you should look for answers that rule out other possible causes. Choice B strengthens the argument by showing that volcanic eruptions occurred frequently before the extinction, but the dinosaurs continued to live. Thus, it is unlikely that the extinction was caused by a volcano and more likely that a meteor caused it. Choice A doesn’t go far enough. Even if the volcanoes are rare, the extinction could have been caused by just one eruption. Choice C doesn’t strengthen the argument. Other scientists’ support of the hypothesis doesn’t address the connection between the conclusion and the premise. Choice D has nothing to do with the argument, while choice E weakens the argument by indicating that a previous comet strike did not lead to an extinction.

KarishmaB · Answer

The OA is a little debatable but not very much.
(C) is certainly not in the running. Just because other people say it, something doesn't become true. You need facts. Most scientists supporting the hypothesis is not a fact that will help me believe the hypothesis. The reason why most scientists support it, might. 
(D) and (E) are irrelevant.

So it comes down to:
A. Volcanoes massive enough to generate high concentrations of iridium are very rare.
B. Massive volcanic eruptions occurred frequently 80 million years ago.

Both support the conclusion to an extent. 
In (A), volcanoes massive enough to generate high concentrations of iridium are rare, not impossible. There could have been one 65 million yrs ago. Hence, it doesn't strengthen our belief in a comet/meteor much.
In (B), massive volcanic eruptions occuring frequently through Earth's history while dinosaurs lived doesn't imply that there couldn't have been an especially huge one which wiped out the dinosaurs. But it does make comet/meteor theory more probable.

Look at the argument again - two things cause concentration of iridium - volcanoes and meteors
Volcanoes occured frequently while dinosaurs lived on Earth. Chances are that an activity which was not usual wiped out dinosaurs. Since dinosaurs were wiped out 65 million yrs ago and there was iridium concentration in rocks which are from 65 million yrs ago, it makes it more likely that a meteor wiped out dinosaurs.

fluke · Answer

I thought it should be "A".

Conclusion:
The meteorite shower is the cause of the dinosaurs' extinction.

The scientists associated high concentration with meteorite shower and meteorite shower with extinction. But, there is no guarantee that high concentration of iridium was indeed due to meteorite shower and not volcanic eruptions.

A- clears the confusion that such high concentration can't be created by eruptions leaving us with only one choice for iridium concentration i.e. meteorite shower.

C- can be another possibility but using the word "cosmic impact" is too broad. Who knows if other scientists hypothesized that the extinction was due to ultraviolet rays(just in case there was no ozone then). Thus, a pure hypothesis by other scientists won't make this argument too strong.

Ans: "A"

But, on a second thought; the word "rare" in A is not too strong. Rare doesn't mean non-existential. Thus, the extinction may have been caused by volcanic eruption.

C becomes the strongest support.

Ans: "C"

"B" actually weakens the argument in a sense and is strict no-no.

siddharthmuzumdar · Answer

I think this is too far a leap to be taken to reach the conclusion. Is this a regular GMAT-like question?

Even I thought the answer would be either A or C. B was totally unexpected.

nikhilsamuel89 · Answer

IMO A. But i'm utterly confused.
The explanation provided by the guide seems to give more weight to the cause of extinction of dinosaurs than to the cause of high iridium levels.
B. Massive volcanic eruptions occurred frequently 80 million years ago. the massive volcanic eruptions may have caused high iridium levels, but the explanation doesn't seem to care about that. It says, if massive eruption were frequent enough(80m years ago) and the dinosaurs were still not extinct(65m years ago), then the eruptions would not have caused the extinction.
Not sure which to give more importance to: the high levels of iridium or the extinction of dinosaurs

OldFritz · Answer

Not a well-framed question but decent practice nonetheless.

Worth noting that even the hardest actual GMAC questions leave you somehow satisfied after reading the explanations/rationale for the correct answer--this particular question doesn't.

Posted from my mobile device

TGC · Answer

P1: Two causes

1. Volcanoes
2. Meteorites/Comets = > Iridium

P2: -65 million yrs , iridium was 30 times the normal

C: M/C => Dinosaurs extinction

Now B Says ,Massive volcanic eruptions occurred frequently 80 million years ago.Moreover,nowhere it is mentioned that they were infrequent (-65) million years.

A. Volcanoes massive enough to generate high concentrations of iridium are very rare.
B. Massive volcanic eruptions occurred frequently 80 million years ago.
C. Most scientists support the hypothesis that a cosmic impact wiped out the dinosaurs.
D. The massive extinction that occurred 70 million years ago killed not only the dinosaurs but also 70 percent of all life on Earth.
E. A comet struck the earth some 120 million years ago, but no widespread extinction occurred.

Poorly framed question

Plz Advice !!

WaterFlowsUp · Answer

Karishma,

Option B comes somewhat closer, but B has flaws:
1. Do we know when for how long dinosaurs existed?
2. 80m years ago meteoric showers were frequent but is that anyhow supports dinosaurs to be killed?

gmatprav · Answer

I sort of agree with OE.

A is quite opposite of what is stated in the stimulus. Stimulus explicitly states that  both  volcanic eruptions and meteors are capable producing extremely high concentrations of iridium. A opposes it. Remember we have to accept what is mentioned in the stimulus as a fact and answers negating the fact in stimulus are not good choices. IMHO.

B states that volcanoes erupted frequently 80 million years ago, this implies two scenarios 1) After sometime volcanic eruptions stopped and therefore can not be the reason for dinosaur extinction. 2) The fact the dinosaurs became extinct around 65 million years means that they survived volcanic eruptions that occurred 80 million years ago. With these two one can conclude that dinosaurs continued to exist after volcanic eruptions and there were no volcanic eruptions when dinosaur extinction occurred. This explanation also identifies comet/meteor as the only source of iridium found in rock stratum from 65 million years ago.

KarishmaB · Answer

Most of it is an inference/assumption. Usually a GMAT question would be clearer but the intent of this question is clear to us through our general knowledge. Dinosaurs lived in the Mesozoic era (between 230 and 65 million years ago)

We need to strengthen the theory that meteors caused extinction, that is, volcanoes did not. If massive volcanoes were common at that time, they probably did not cause the wipeout. 
(A) tells you that very massive volcanoes are rare but it doesn't say they don't occur. Hence it doesn't say that volcanoes probably did not cause the extinction. In fact, if very massive volcanoes are rare, a rare instance could very well have caused the extinction of the species.

geezer0305 · Answer

I think the explanations for Choice A and B contradict each other:

"Choice A doesn’t go far enough. Even if the volcanoes are rare, the extinction could have been caused by just one eruption."  By this logic used to eliminate choice A, one can say that although massive volcanoes occurred 80 million years ago without resulting in extinction, one giant unfathomably supernormous volcano did the trick 65 mill yrs ago. Answer choice B leaves equal room for doubt as does choice A. Answer choice C strengthens the argument by adding credibility to the scientist's claim.

prayritgates · Answer

Read Power Score CR Bible those who supports "C".

It clearly says: "Eliminate any alternate cause for the stated fact"

As argument clearly states only meteor or comet (or somewhat about Volcanic eruptions):

"they concluded that a massive meteor or comet hit the Earth and caused the massive extinction of the dinosaurs"

"Cosmic bla bla" is clearly an alternate cause. Though should be eliminated.

As (D) and (E) are already out of scope, so lets get back to (a) & (b):

(a) states "power or strength of eruption" which is clearly out of scope as conclusion is clearly about WHO CAUSED?

Hence, (B) is the choice.

"Work on process on elimination with strong ground to account on, really will give positive results on these types of problems"

Nevernevergiveup · Answer

Iridium, a hard, whitish metal similar to platinum, is extremely rare on Earth. Extremely high concentrations of iridium on Earth result from only two scenarios: massive volcanic eruptions that release iridium from deep within the Earth and meteorites that shower down on Earth from space. When scientists found concentrations of iridium 30 times higher than normal in rock stratum from 65 million years ago, they concluded that a massive meteor or comet hit the Earth and caused the massive extinction of the dinosaurs.

Which of the following, if true, most strongly supports the scientist’s conclusion?

A. Volcanoes massive enough to generate high concentrations of iridium are very rare. 
 not impossible and we are not sure it cannot be a possibility at 65 million years.

C. Most scientists support the hypothesis that a cosmic impact wiped out the dinosaurs.
 (most scientists supporting a theory does not validate it.)

E. A comet struck the earth some 120 million years ago, but no widespread extinction occurred.
 (no extinction and 120 years ago does not help our conclusion.)

Between B and D,

B. Massive volcanic eruptions occurred frequently 80 million years ago.
 (This explains the scenario 80 million years ago but what about 15 million years later.) 
D. The massive extinction that occurred 70 million years ago killed not only the dinosaurs but also 70 percent of all life on Earth.
 (this just says extinction but it does not say what might be the cause for it. Is it volcano or comet)

SVaidyaraman · Answer

B is correct only if it is known that massive volcanic eruptions could cause the extinction of dinosaurs. I think the passage is not focused and the conclusion is not well developed.

hellosanthosh2k2 · Answer

Hi Karishma,
 I initially chose A over B. 
 I have one query.
office explanation says for B, massive valcanoes eruption happened 80 milliions years ago and    , which means massive valcanoes are not enough to extinct dinosaurs. so only cause to extinction is comet.

But that highlighted portion in red is not mentioned in the passage. It is rather assumption on which official explanation for choice B lies. But this assumption need not be true, maybe, comet did strike 65 milliions years ago but before that a single massive massive valcano could have extincted all dinosaurs.

am i thinking correct?

KarishmaB · Answer

Dinosaurs became extinct 65 million years ago. That is why the hypothesis links high level of iridium found 65 million years ago with dinosaur extinction. They could not have become extinct 80 million years ago.

ayushgmatclub1 · Answer

What if there were indeed frequent volcanic eruptions around 80 million years ago and they decreased the dinosaur population, and the one that erupted 65 million years ago wiped the entire remaining population out? Hence B can be proved wrong.

Official answers are air tight, they do not force you to assume a lot and do not leave much gap for your correct logical thoughts to stand against the correct answer, hence I do not think that this question is good enough.

Amandhanani2627 · Answer

Should Option B state "Massive Volcanic eruptions occurred frequently more than 80 million years ago" ? I mean the current option B does imply anything about massive volcanic eruptions after 80 million years.

arya251294 · Answer

Nowhere it is mentioned that the dinosaurs got extinct 65 million years ago.
The argument just tells us that the iridium content was higher than normal in the rock stratum that was from 65 million years ago.

Iridium, a hard, whitish metal similar to platinum, is extremely rare

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Critical Reasoning (CR) Questions

Iridium, a hard, whitish metal similar to platinum, is extremely rare

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards